1. Field of the Invention
The present invention relates to sterilization of containers. Specifically, the present invention relates to an apparatus and method for the sterilization of containers using multiple applications of heat and hydrogen peroxide gas within a sterilization tunnel.
2. Description of the Related Art
Milk or juice is often packaged in containers that have been sterilized to prolong shelf life of the contents under refrigeration. When milk or juice is being packaged under aseptic packaging conditions, the contents are capable of being stored for a substantial period of time at room temperature without spoilage. Such packaging processes require effective sterilization of the packaging material prior to filling of a container formed from the packaging material. For example, a container, such as a gable-top carton, that has previously been partially formed may have its interior surfaces sterilized prior to being filled with product. U.S. Pat. No. 4,375,145, discloses a packaging machine having a conveyor on which pre-formed cartons advance under ultraviolet germicidal solution, such as hydrogen peroxide, passing under the ultraviolet lamps.
A popular type of packaged product is an Extended Shelf Life ("ESL") packaged product due to the added value such a filled container presents to a retailer. For example, pasteurized milk processed and packaged under typical conditions has a shelf life at four degrees Celsius of seven to fourteen days while the same milk processed and packaged under ESL conditions has a shelf life of fourteen to sixty days. Under ESL conditions, juice may have a shelf life of forty to one-hundred twenty days, liquid eggs sixty to ninety days, and eggnog forty-five to sixty days. Thus, ESL packaging greatly enhances a product since it extends the time period that the particular product may be offered for sale to the consuming public. In order to have ESL filling, the filling system should be kept sterile in order to prevent contamination of the product or container during filling on a form, fill and seal package machine.
Many ESL machines use UV light and hydrogen peroxide. However, UV lamps greatly increase the price of a packaging machine and require extensive monitoring and maintenance to operate properly.
Another problem with current sterilization practices is the limitation of concentration of hydrogen peroxide that may be used on packaging material for food. Only a minute quantity of hydrogen peroxide residue may be found on the packaging that limits most applications to less than 1% concentration, and requiring UV light. However, as mentioned above, UV lamps and associated components are very expensive and require more maintenance and energy than machines without UV lamps.
Another popular type of packaged product is an aseptic packaged product due to the tremendous value such a filled container presents to a retailer. For example, ultra high temperature processed milk may have a non-refrigerated shelf life of over one-year in a TETRA BRIK.RTM. Aseptic package. Such a package is fabricated from a web of packaging material on a vertical form, fill and seal packaging machine that is substantially enclosed except for an outlet for the final package. It is quite apparent that producing a package capable of non-refrigerated distribution is highly desirable, however, the packaging machine must be substantially enclosed to prevent any and all contamination of the product, the machine or the packaging material.
In the area of aseptic linear form, fill and seal packaging machines, wherein a series of container blanks are utilized instead of a web of packaging material, the maintenance of the entire machine in a non-contaminated enclosed environment is highly critical. One such machine is disclosed in U.S. Pat. No. 5,660,100 wherein a preheating zone, a sterilizing zone, a drying zone, a filling zone and a closure zone are all enclosed within a single sterile space that optimizes hermeticity. A hydrogen peroxide aerosol or liquid is utilized to sterilize the packages and the enclosure. As is apparent, the hermetically sealed environment is the most important factor in maintaining the aseptic environment. Such an environment increases the price of the machine and requires substantial maintenance.
Another machine is disclosed in U.S. Pat. No. 4,992,247 wherein a container sterilization system is adaptable to a form, fill and seal machine. The system is a closed loop system having a chamber, a blower for directing a mixture of air, vaporized hydrogen peroxide and vaporized water through ductwork and to a vapor delivery inlet manifold disposed above a line of conveyors conveyed therethrough the system. An exhaust manifold is positioned below the containers to receive the mixture. An iso-box is positioned at the front of the inlet manifold to serve as an air lock or curtain to prevent outside contaminants from entering the chamber and to prevent vaporized hydrogen peroxide from leaving the chamber. Containers enter the iso-box before entering the chamber. In the chamber, hydrogen peroxide condenses on the inner surfaces of each of the containers prior to exiting through another iso-box. As each container moves through the chamber, liquid hydrogen peroxide condenses on inner surfaces and eventually an equilibrium is reached between the liquid and vapor hydrogen peroxide. The pre-heating temperatures and the processing temperatures are controlled to maintain the sterilizing effect. After the iso-box is a drying air inlet manifold having heated air flowing from a HEPA filter. Although U.S. Pat. No. 4,992,247 discloses that the system is positioned between a bottom forming station and a top sealing station, it is assumed that a filling station is disposed adjacent the drying manifold. It is important in U.S. Pat. No. 4,992,247 that the hydrogen peroxide condense on the containers in order to have the desired "scrubbing" effect.
An ESL machine is capable of producing a large number of containers per hour of operation and allows for an "open" operating environment as compared to an aseptic machine that requires a substantially enclosed environment for most of the machine to prevent contamination of the packaging material, product and machinery. However, the aseptic container is capable of non-refrigerated storage for long periods of time. In the sterilized package stage, positioned between ESL packages and aseptic packages, are high acid ambient distribution ("HAAD") packages. The HAAD package is capable of non-refrigerated storage, however, the product must have a minimum acidity (pH less than 4.6) such as the acidity of orange juice (pH 2.8) as compared to the acidity of milk (pH 6.9) which is an unacceptable product for a HAAD package. What is needed is a way of producing a HAAD container on a linear form, fill and seal packaging machine without major modification of the machine.